Botany Basics: Symmetry

Flowers are easily the most variable organs of flowering plants (hence the name), and botanists are interested in the mfor a variety of reasons, not least because of their value in systematics (my field). The great diversity of floral forms makes for lots of information as to what plants are closely related. A lot of work has been done in genetics on what determines the identities of the organs in a flower (why one the flowers of one species have both male and female reproductive parts while others have only one or the other, for example). More recent work has begun to focus on how the shapes of flowers are genetically determined, and more specifically, their symmetry. But what do botanists mean by 'symmetry'?

Botany Basics: Carpels

In 1790, the German poet J.W. von Goethe introduced the hypothesis that all the parts of a flower are derived from modified leaves. On this view, the sepals (the green, sheathing structures on the pink pictured above) and petals of a flower are leaves which surround the reproductive parts, usually with the goal of attracting insect pollinators, with an optional dose of attractive pigment. The stamens (male reproductive structures) are leaves which have developed specialized pollen-producing organs. The stamens in the water-lily pictured (the yellow structures) are more or less leaf-like, and it is easy to see how they might have developed from a primordial leaf. But where are the leaves on a pistil?